Humoral Immune Activation Against Mycobacterium avium subsp. paratuberculosis Through Oral Immunization with Engineered Salmonella

Attenuated Salmonella strains offer an opportunity for delivering DNA vaccines to antigen-presenting cells. DNA vaccines trigger cellular immune responses, making them suitable for targeting intracellular pathogens, such as Mycobacterium avium subspecies paratuberculosis (MAP). Since whole organism MAP vaccines interfere with tuberculosis diagnosis, innovative vaccine technologies have been introduced to elicit an immune response targeting species-specific antigens. Fibronectin attachment protein (FAP), a MAP surface antigen that is species-specific, can induce cellular immune responses. The present study aims to explore the immunogenic potential of a mammalian expression plasmid encoding the fap-P gene of MAP within a mouse model, utilizing a Salmonella vector for oral immunization using a fluorescent assay and Western blot analysis. The results proved the ability of the constructed plasmid to stimulate the humoral immune response in mice. Moreover, fluorescence microscopy of splenocytes confirmed the successful delivery of the plasmid to the immune system at 24, 48, and 72 h following oral administration. It can be concluded that FAP-P could be considered a candidate for further investigation in the context of MAP vaccine development. Additionally, the use of Salmonella as a delivery system not only improves the efficacy of DNA vaccines but also helps in the preliminary evaluation of the antigens’ immunogenic properties.